I was recently admitted for UCL for their PPE (Philosophy Politics Economic) program, as well as McGill for their Arts&sciences, Arts, Engineering and Business programs. I’ve only visited Montreal and really loved it, but UCL is far more prestigious. Ho do both colleges compare in term of career opportunities?
Congrats on your acceptances! PPE at UCL is very competitive, so well done 
If money is not an object, I would go to UCL, especially for PPE.
My daughter just got back from an open house at UCL and she is very happy with what she saw.
Prestige depends on who you ask and where you are. In the US, most people would not have heard of UCL while some folks know that McGill is one of the 2 best unis in Canada.
Career opportunities also depend on where you are authorized to work. Where would that be?